Hydrogen based refrigeration process using an electrochemical compressor
The evaporation of liquids (e.g. water) in the air is a well-known cooling method. This effect can be used in a hermetically sealed cycle in which a carrier gas transports vaporous refrigerant from an evaporation point via an internal heat exchanger to a condensation point. The evaporative heat exchanger absorbs heat from the cold room and transfers it to the surface wetted with liquid refrigerant, which evaporates at a low temperature. The carrier gas saturated with vaporized refrigerant is then heated in the internal counterflow heat exchanger to close to condensation temperature. In the condensation heat exchanger, the carrier gas is removed from the gas mixture, causing the partial pressure of the refrigerant to rise to the condensation pressure at the high temperature present. As a result, the refrigerant begins to condense, releasing the heat into the environment via the heat exchanger. To do this, the carrier gas must be effectively separated from the refrigerant after the condenser and recompressed to a higher pressure. The liquid refrigerant and the compressed carrier gas are finally cooled in the internal heat exchanger and fed back to the evaporative heat exchanger. The refrigeration process described here uses the working pair hydrogen and R600a as carrier gas and refrigerant respectively. An electrochemical H2 membrane compressor is proposed for separation and compression. The advantage of this compressor is that it operates with absolutely no vibrations or noise emissions. This system is therefore suitable for use as a so-called “hotel refrigerator” in bedrooms or other acoustically sensitive areas. It achieves significantly better performance figures than the absorption-diffusion refrigerators currently used for this purpose. This paper describes the underlying calculation model and uses it to derive the thermodynamic relationships for different operating conditions. The results are used for a basic design of the components. In particular, the design of the H2 compressor is discussed and current data from research on achievable mass flows, pressures, pressure differences, separation efficiencies and efficiency as well as cooling capacity, temperatures and coefficient of performance of the cooling unit are described.